Various forms of platform assemblies for slanted ladders have been devised to provide a substantially horizontal surface on which workmen may stand or equipment may be placed. Such platforms are particularly applicable to ladders laid directly on a pitched roof surface and held in place by hooks over the crest of the roof. They are applicable as well, however, to ladders which lean against vertical surfaces. Portable adjustable roof platforms described in U.S. Pat. Nos. 1,549,647 and 4,450,935 are typical of such prior art devices.
Conventional platform assemblies include a base adapted to be hooked to and lie against rungs of a ladder and a platform hinged to the base. Some form of brace is then provided between the platform and the base to hold the platform and base at an included angle which substantially levels the platform. Prior art adjustment means are known for varying this included angle and the present invention is directed to improvements in such adjustment means.
In U.S. Pat. No. 4,450,935, for example, the adjustment means consists of a crank and screw which operate a toggle on the brace. The crank and screw device, however, is susceptible of inadvertent turning because of its exposed position on the assembly. Also the brace underlies the platform at closely spaced points so that the platform has what approaches a three-point support rather than a four-point support and therefore lacks optimum stability. The design of U.S. Pat. No. 1,549,657 provides hooked bars and locking means for adjustment which are somewhat complicated and clumsy to operate. In addition the support given by the brace to the platform in that design has the instability of a three-point support.
The prior art platform assemblies are dificient in that they involve either complicated manipulation for adjustment or are subject to unintentional operation of the adjustment means or provide insufficient stability to the platform.